Citation
Review of Broward County beach nourishment project : Segments II and III

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Title:
Review of Broward County beach nourishment project : Segments II and III
Series Title:
Review of Broward County beach nourishment project : Segments II and III
Creator:
Dean, Robert G.
Place of Publication:
Gainesville, Fla.
Publisher:
Coastal & Oceanographic Engineering Dept. of Civil & Coastal Engineering, University of Florida
Language:
English

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University of Florida
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University of Florida
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All applicable rights reserved by the source institution and holding location.

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UFL/COEL-2003/004

REVIEW OF BROWARD COUNTY BEACH NOURISHMENT PROJECT: SEGMENTS II AND III by
Robert G. Dean

Submitted to:
Bureau of Beaches and Wetland Resources Department of Environmental Protection Tallahassee, FL 32399

June 27, 2003




REVIEW OF BRO WARD COUNTY BEACH NOURISHMENT PROJECT: Segments 11 and III
June 27, 2003
Submitted to:
Bureau of Beaches and Wetland Resources Department of Environmental Protection Tallahassee, FL 32399
Submitted by: Robert G. Dean Department of Civil and Coastal Engineering University of Florida Gainesville, FL 32611 6590




Table of Contents
EXECUTIVE SUMMARY ...................................................................................................... 1
REVIEW OF BROWARD COUNTY BEACH NOURISHMENT PROJECT: Segm ents II and III ...................................................................................................................... 2
1 INTRODUCTION and SCOPE of REVIEW ................................................................... 2
2 REVIEW RESULTS ....................................................................................................... 2
2a) Overall Project Description ........................................................................................ 2
2b) Project N eed ........................................................................................................... 4
2c) Project D esign ......................................................................................................... 5
2c-1) Volumes to be Placed ..................................................................................... 5
2c-2) Nourishment Sediment Characteristics ............................................................ 5
2c-3) Project Longevity ............................................................................................. 6
2d) Effect of Borrow Area I on Stability of Deerfield Beach .......................................... 7
2e) Environmental Considerations ................................................................................... 8
3 SUMMARY and CONCLUSIONS ................................................................................. 10
4 RE FE R EN C E S ................................................................................................................... 10
... . ,,................,, ., . ., . ,*.... . .. .............. .... ..... . . . . .... . ..* . ... .
List of Tables
1 Summary of Characteristics of Broward County Beach Nourishment Project ............. 4
2 Summary of Sediment Characteristics in Borrow Areas and Natural Sediments ......... 5
3 Results of Simulation Calculations for Four Scenarios ............................................ 6
4 Characteristics of Borrow Areas Off Deerfield Beach and Anna Maria Key ............. 10
List of Figures
1 Beach Nourishment Project Limits and Borrow Areas ............................................ 3
2 Profile Through Monument R-2 in Broward County Showing Pre-1998, Post-1998 and
Maximum Future Removal of Sediments ............................................................... 9
3 Profile Through R-26 in Manatee County Showing Pre- and Post-Excavation for the
1993 Beach Nourishment of Anna Maria Key ....................................................... 9




EXECUTIVE SUMMARY

This report provides a technical review of the planned beach nourishment of 11.7 miles of Broward County's beaches. The beaches planned for nourishment have been listed as "critically eroded" by the Florida Department of Environmental Protection. In addition to nourishment, the comprehensive program includes bypassing around Port Everglades Entrance and the construction of three structures immediately south of Port Everglades Entrance, an area of extreme erosional stress.
This review addresses: (a) Overall project description, (b) Project need, (c) Project design, (d) Effects of excavation from Borrow Area I on the stability of the beaches of Deerfield Beach, and (e) Environmnental considerations.
The project is justified due to the degree of erosion and the known linkage between wide beaches and damage reduction due to severe storms and tourism visitation and the economy of Broward County. The Project design was evaluated and the six-year renourishment interval was confirmed qualitatively if full bypassing around Port Everglades Entrance is implemented. The effect of the excavation of sediment from Borrow Area I which lies off Deerfield Beach was examined through comparison with another borrow area in Florida and on the basis of research conducted at the University of Florida. It was determined that the substantial groin field immediately landward of the borrow area coupled with the bypassing at Boca Raton Inlet are such that no significant effects on the shoreline of Deerfield Beach are anticipated. Environmental concerns have been resolved through a number of efforts including: (1) removing two potential borrow areas (Borrow Areas V and VII were removed from further consideration), (2) Decreasing the size of the project, (3) increasing the dredging buffer around reefs and other sensitive resources, (4) extensive postnourishment monitoring programs, and (5) mitigation through placement of limestone rocks to replace nearshore hard bottom covered by the nourishment.
As an overall summary statement, it is concluded that the project is necessary, well designed and can be constructed without significant impacts to the beach system or environent. The implementation of bypassing around Port Everglades Entrance is a critical element of the future program of managing the beaches of Broward County.




REVIEW OF BROWARD COUNTY BEACH NOURISHMENT PROJECT: Segments 11 and III
1. INTRODUCTION AND SCOPE OF REVIEW
Broward County has developed a comprehensive beach nourishment program for Segments II and III of the County's overall shoreline. The nourishment comprises placement of 2.47 million cubic yards along 11. 7 miles of the County' s 24 mile shoreline. The Florida Department of Environmental Protection has certified 21 miles of the County shoreline to be critically eroded. The sand will be dredged from 5 borrow pits located from 1,200 feet to 4,500 feet from the shoreline and lying between the three parallel reefs which are aligned approximately parallel to the shoreline.
The Bureau of Beaches and Wetland Resources (BBWR) of the Florida Department of Environmental Protection (FDEP) has requested this review of the technical aspects of the Project. Specifically, the review addresses: (a) Overall project description, (b) Project need, (c) Project design, (d) Effects of excavation from Borrow Area I on the stability of the beaches of Deerfield Beach, and (e) Environmental aspects. In reviewing each of these, the basis for the assessment will be provided.
2. REVIEW RESULTS
Each of the Review tasks is addressed in the following sections.
2a) Overall Project Description
The Broward County Beach Nourishment Project is a Federally authorized project in which nourishment costs are shared by Federal, State and Local governmental agencies. The Federal authorization for this project was provided in 1965, encompasses all 24 miles of the County shoreline and comprises three segments, only two of which (Segments 11 and III) are included in the present project. The three segments of the overall project are shown in Figure 1 as are the borrow areas (labeled BA). The overall program includes bypassing around Port Everglades Entrance and installation of three shore stabilization structures (one spur on the south jetty of Port Everglades Entrance and two groins immediately south of the Entrance).
The portions of Segments II and III which comprise the present project include the four reaches summarized in Table 1.




_A*IllGULf OF MEX/CO
H.SBO INtEl l

BEACH FILL LIMITS
ATLANTIC
GROIN FIELD ACH FILL UITS 0 CEAN
N.T.S.

Figure 1 Beach Nourishment Project Limits and Borrow Areas.




Table 1

Summary of Characteristics of Broward County Beach Nourishment Project

Segment Description Lengths to be DEP Volumes to be Hard Bottom
of Reach Nourished Monuments Placed Impact (Acres)
(Miles) (yd3)
II Pompano Beach/ 1.0 R-37 to R-42 198,000 3.0
Lauderdale by the
Sea
II Fort Lauderdale 13.9 R-51 to R-71 732.200 1 3.0
II Totals for Segment 4.9 930,200 6.0
II117
III John U. Lloyd 1.6 R-86 to R-94
State Beach
Recreational Area
III Hollywood/ 5.2 R-101 to R-128
Halandale
III Totals for Segment 6.8 1,540,000 7.6
III T

2b) Project Need

The FDEP has certified that 21 miles of the 24 miles of Broward County's shorelines are "critically eroded" and there are some areas where there is very little beach at high tide. Obviously, these areas are vulnerable to damage by severe storms. Broward County has a history of beach erosion and beach erosion control measures which have been generally effective. The strong links between wide beaches and storm damage reduction and tourism have been well established in Florida in general and in Broward County in particular. The design of the beach nourishment project is based on storm damage reduction.
As a summary statement, it is evident that the Project is needed to protect upland structures during severe storms and for the beaches to continue their contributions to the economy of Broward County.




The elements of the Project have been presented in Table 1. The following aspects of the design have been evaluated: (1) Volumes to be placed, (2) Sediment characteristics, and (3) Project longevity.
2c-1) Volumes to be Placed
As noted, a total of 2.47 million cubic yards will be placed over a combined beach length of 11.7 miles. The volumes vary along the project length depending on the beach condition at the particular section. An average of approximately 40 cubic yards of sand per foot of beach length will be placed. This is a reasonably modest density of placed sediment; however, the beach nourishment length and synergism of the lengths will add to the overall project longevity. In summary, the volumes planned for placement appear reasonable considering the beneficial effects of synergism, the ongoing sand bypassing at Hillsboro Inlet and the plans to bypass sand at Port Everglades Entrance.
2c-2) Nourishment Sediment Characteristics There are two aspects of the nourishment sediments relevant to design. The first is the proportion of silts and clays that could cause excessive turbidity. The overall percentage of silts and clays (smaller that 62 microns) in the borrow areas is 2.2 % and the average percentage for the present beach is 1.2 %. Summary results are presented in Table 2. The 2.2% is considered small.
Table 2
Summary of Sediment Characteristics in Borrow Areas and Natural Sediments
Available Beach
Borrow Area or Natural Average Percentage Mean Sediment Compatible Sand
Conditions Silts and Clays (%) Size (mm) (cubic yards)
1 2.0 0.39 1,529,000
11 1.9 0.31
111 4.4 0.43 495,000
IV 2.6 0.31 28,000
VI 2.1 0.42 99,000
Average for Borrow Areas 2.23 0.35
Natural Beach, Segment 11 1.3 0.31 N/A
Natural Beach, Segment 111 1.1 0.34 N/A
1 Average for Natural Beaches 1.2 0.33 N/A

2c) Project Design




The second sediment attribute that is relevant to design is the overall sediment size characteristics. Nourishment sediments that are finer than those naturally present on the beach tend to have a profile that is milder in slope resulting in a narrower dry beach than if sediment with the natural characteristics had been used. Additionally, smaller sediments are transported by the waves more readily and thus the project would have a shorter longevity. The overall representative sediment size (mean size) of the sediments present in the beach system was determined to be 0.33 mm and the representative median sizes for the five individual borrow areas are as shown in Table 2 with a mean for all five borrow areas of 0.35 mm. Thus, the nourishment sediment sizes are adequate.
2c-3) Project Longevity
The project is planned for a six year renourishment interval. To provide an approximate evaluation of the Project longevity, a numerical model (Dean and Grant, 1989) developed for the BBWVR (although this agency had a different name then) was applied. Four cases were considered for the planned nourishment characteristics: (A) No background erosion and no bypassing around Port Everglades Entrance, (B) Uniform background erosion of one foot per year and no bypassing around Port Everglades Entrance, (C) No background erosion and full bypassing around Port Everglades Entrance, and (D) Uniform background erosion of one foot per year and full bypassing around Port Everglades Entrance. The results of these simulations, which are approximate, are presented in Table 3. The results in Table 3 represent the percentage of sediment remaining within the placement areas after six years of representative wave conditions. These cases consider a net southerly longshore sediment transport of 100,000 cubic yards per year.
Table 3
Results of Simulation Calculations for Four Scenarios
Percentage of Placed Sediment Remaining in Case Six Years in the Following Placement Areas
R- 37 to R-51 to R-86 to R-101 to R-42 R-71 R-94 R-128
(A) No Background Erosion and No
Bypassing Around Port Everglades Entrance 50% 87% 93% 90%
(B)Uniformn Background Erosion of 1 foot
per year and No Bypassing Around Port
Everglades Entrance 38% 73% 197% 79%
(C) No Background Erosion and Full
Bypassing Around Port Everglades Entrance 50% 87% 67% 90%
(D)Uniform Background Erosion of 1 foot per year and Full Bypassing Around Port
Everglades Entrance 38% 73% 55% 79%




The stabilizing effects of the T-head groins and spur were not included in the simulation results presented in Table 3. Two conclusions derive from the results in Table 3. First, for the case of full bypassing around Port Everglades Entrance, there is reasonable qualitative agreement with the six year planned renourishment interval in the sense that substantial proportions of sediment are predicted to remain in the nourishment areas for no background erosion and a background erosion rate of 1 foot per year. Secondly, the need for bypassing around Port Everglades Entrance is emphasized by comparison of the results for the area immediately south of Port Everglades Entrance (R-86 to R-94) for the cases of with and without bypassing. Although not evident from the results in Table 3, the sand "lost" from the nourishment areas is not lost from the system but rather has spread out along the shoreline, lessening the need for future renourishments of the overall system.
2d) Effect of Borrow Area I on Stability of Deerfield Beach
The inner edge of Borrow Area I lies approximately 1,200 feet from the Deerfield Beach shoreline in approximately 22 feet of water. This borrow area lies between the first and second reefs with a third reef lying farther seaward. Approximately 550,000 cubic yards had been removed from this borrow area in 1998 for nourishment of Deerfield Beach. The planned nourishment would remove up to a maximum additional 1,000,000 cubic yards if found to be needed for the Project.
Potential effects are due primarily to the change in wave characteristics caused by the depth increases over the borrow area. Two fairly detailed studies have been conducted to evaluate the effects of removal of material from Borrow Area 1. The earlier study was conducted by Coastal Systems International (CSI, 1998) and the more recent by Applied Technology and Management (ATM, 2001), both respected coastal engineering consulting firms. The two studies examined different dredged depths with CSI and ATM considering dredged depths on the order of 6 feet and 19 feet below the ambient depths in the borrow area respectively, both appropriate at the times of the considered dredging. A complete analysis of this problem requires examining both the changes in wave patterns and the resulting effects on the nearshore area and shoreline.
Both studies were conducted with numerical models and both studies used the same numerical model for predicting the changes in wave patterns due to the increased depths in the borrow area. The second study also applied a numerical model to investigate potential sediment transport and shoreline changes.
Although an exact comparison of the two study results is difficult, it appears that both models are in reasonable agreement as to the effects of the borrow area on the changes in the wave system as the waves move over the deepened borrow area. The more recent study indicated substantial potential changes to the Deerfield Beach shorelines.
As background for the following assessment of this issue, the BBWvR has funded research at the University of Florida on the effects of borrow areas on the adjacent beaches. We have investigated these effects, both in the laboratory and through survey data documenting the performance of beach nourishment projects. The results of our studies have established that the effects of borrow areas on adjacent shorelines are fairly subtle in Florida settings. The field situation most




similar to the borrow pit off Deerfield Beach of which I am aware is that off Anna Maria Key in Manatee County. This borrow area was excavated in 1993. Figures 2 and 3 present profiles through Borrow Area I at Deerfield Beach and the borrow area off Anna Maria Key, respectively. Table 4 summarizes the characteristics of these two borrow areas.
Analysis of the Anna Maria project evolution indicated some anomalies from the predicted performance; however, these were relatively small (Dean, et al, 1999, Wang and Dean, 2001). Although the ATM study of Borrow Area I off Deerfield Beach suggested that there could be significant effects attributable to the borrow pit, it is relevant that their predicted changes were couched in terms of "potential changes" or "potential effects". They did not carry the sediment transport calculations through to actual shoreline changes nor did their analysis recognize the rather extensive T-head groin system consisting of 55 groins which protects the Deerfield Beach shoreline. Additionally, the shoreline change model employed by ATM does not include a transport contribution from the longshore variation in wave height. A University of Florida Ph. D. dissertation (Bender, 2003) has established that this second term tends to balance the first term (the first term was the only term included in the ATM study). Although one might expect that the ATM study would have included an evaluation of the 1998 deepening of the borrow area on the shoreline stability for calibration/evaluation purposes, they did not and could not have as the Deerfield Beach shorelines are in a better condition today than they were prior to the 1998 nourishment during which sand was removed from the borrow area.
An attempt has been made here to carry through the ATM results to determine the potential shoreline changes accounting for the changes in longshore sediment transport determined by ATM. This effort recognizes the effects of the groin field. These results indicate that any shoreline changes in the vicinity of Borrow Area I will be less than 10 feet as a result of dredging this borrow area. The basis for these calculations considers that the shoreline position is such that it interacts with the groins which are spaced at approximately 100 feet.
2e) Environmental Considerations
There are several environmental considerations associated with the planned beach nourishment project. These all appear to have been resolved to the satisfaction of the various regulatory agencies and Broward County. Changes leading to resolving these issues include; (a) removing two potential borrow areas (Borrow Areas V and VII were removed from further consideration),
(b) Decreasing the size of the project, (c) increasing the dredging buffer around reefs and other sensitive resources, (d) extensive post-nourishment monitoring programs, and (e) mitigation through placement of limestone rocks to replace nearshore hard bottom covered by the nourishment.




20
'Pr'-t19 99 Pro:Tle
0-20
-40 ",- ' A
4 ax imi im Cul JT
-40 0 400 800 1200 1600 2000 2400 2800
Distance in Feet
Figure 2. Profile Through Monument R-2 in Broward County Showing
Pre-1998, Post-1998 and Maximum Future Removal of Sediments.
20
1 0 .............." ................. ....... .. . . . . . ............................ .
10
'/' ; : -- Decermber 1992
October 1993
,, ... .. ..i\. :.. .. .. ... ... ... .. ... ... ... . .... .. M ay 1994I. .
0
~-0
.......... .... ....... .................... ........... .............................
-10 ..........
W.-20 ............ ............ ... .
..-. .. . ...0.. . ..................... ...... . . "' . . . .
-40
0 1000 2000 3000
Distance From Monument (ft) Figure 3. Profile Through R-26 in Manatee County Showing Pre- and Post
Excavation for the 1993 Beach Nourishment of Anna Maria Key.
10




Table 4

Characteristics of Borrow Areas Off Deerfield Beach and Anna Maria Key
Distance From Water Depth Approximate Dredge Project Shore (ft) (ft) Depth Below Width Length
Ambient (ft) j ft) (lfll)
Deerfield Beach 1 ,1 200 22 1 up to 19 1 1,100 4,300
Anna Maria Key 1,400 20 10. 1,000 90
3. SUMMARY AND CONCLUSIONS
The design of the Broward County beach nourishment project has been reviewed with emphasis on its technical characteristics. Additionally, the potential effects of Borrow Area I offshore of the Deerfield Beach shoreline have been examined by comparing with other borrow areas and by extending the potential longshore sediment transport changes determined by Applied Technology and Management to include the stabilizing effects of the substantial groin field along the shoreline of Deerfield Beach.
It is concluded that the Project design is both needed to reduce the jeopardy of upland investment to future severe storms and to enhance the contribution of the beaches to the economy of the County. The characteristics of the nourishment sediments are appropriate and independent calculations of the project evolution were carried out and agreed qualitatively with the design six year renourishment interval. It is stressed that the success of the comprehensive plan is dependent on reinstating the natural sediment transport around Port Everglades through bypassing.
Examination of the potential effects of removal of sediment from Borrow Area I on the beaches of Deerfield Beach results in a very minimal effect when accounting for the stabilizing effects of the substantial groin field. This is supported by the lack of identifiable adverse effects due to the 1998 removal of material from this borrow area.
4. REFERENCES
Applied Technology and Management (2002) "Broward County Borrow Area Wave Impact Study: City of Deerfield Beach," September.
Bender, C. J. (2003) "Wave Transformation by Bathymetric Anomalies With Gradual Transitions in Depth and Resulting Shoreline Response," Ph. D. Dissertation, Department of Civil and Coastal Engineering, University of Florida, Gainesville, Florida, 237 pages.
Coastal Systems International (1998) "Wave Propagation Modeling," 21 pages.




Dean, R. G. and J. Grant (1989) "Development of Methodology for Thirty-Year Shoreline Projections in the Vicinity of Beach Nourishment Projects," UFL/COEL-89/026, Coastal and Oceanographic Engineering Department, University of Florida, Gainesville, FL.
Dean, R. G., R. Liotta and G. Simon (1999) "Erosional Hot Spots," UFL/COEL-99/021, Coastal and Oceanographic Engineering Department, University of Florida, Gainesville, FL.
Dean, R. G. (2002) "Beach Nourishment: Theory and Practice", World Scientific, Singapore, 399 Pages.
Wang, Z. and R. G. Dean (2001) "Manatee County Beach Nourishment Project: Performance and Erosional Hot Spot Analysis", UFL/COEL-2001/003, Coastal and Oceanographic Engineering Department, University of Florida, Gainesville